Conventionally, a piano, an accordion, an organ, an electronic instrument or other keyboard instrument is efficiently manufactured by injection molding acrylic resin or other synthetic resin.
The keyboard instrument is, however, played by a relatively large number of people when it is installed, for example, at school, and bacteria are conveyed from person to person via fingers and thumb. Recently, people increasingly had a liking for cleanliness. Therefore, keyboard instruments have also been demanded to be always clean.
People not only play the keyboard instrument but also own it as a piece of interior decoration. Therefore, the keyboard instrument is demanded to be firmly prevented from being discolored by grown bacterial.